This invention relates to a cylinder pump used for automatic chemical analyzers or the like.
The automatic chemical analyzer is an apparatus which can automatically analyze a sample for biochemical inspection thereof. Particularly, it is used to analyze a number of test specimens quickly and accurately for a wide variety of inspection items. FIG. 5 illustrates a typical analyzer of this type. The analyzer comprises sampling pumps 1, distributing nozzles 2 coupled to the sampling pumps 1 through tubes, a number of serum samples 3, a reaction trough 4 with a number of reaction cells 4a accommodating the test specimens, a nozzle 5 for charging a reagent into the reaction cells, an optical measuring section 6 including light sources 6a, reflecting mirrors 6b and light-receiving sections 6c, and a control section 7 including an operation panel 7a, a CPU 7b and an operational section 7c. The sampling pumps 1, distributing nozzles 2, reagent charging nozzle 5 and optical measuring section 6 are driven under the control of the control section 7. Data representing the quantity, number, position, etc. of serum samples is input from the operation panel 7a to the CPU 7b. The total quantity of serum withdrawn by the distributing nozzles 2 is calculated by the CPU 7b and operational section 7c, and the CPU 7b produces a signal showing the calculated quantity of serum. According to this signal, a driver for the sampling pumps 1, which includes a pulse motor 1a, a lead screw 1b and a plunger retainer 1c, is driven, whereby a predetermined quantity of serum samples 3 is sucked in through the distributing nozzles 2. The nozzles 2 are then moved to a predetermined discharge position in the reaction trough 4 and discharge the serum into corresponding reaction cells 4a. A reagent X is poured through the reagent charging nozzle 5 into the reaction cells, and the resultant mixture is agitated to cause reaction. The mixture is transferred to the optical measuring section 6 for optical analysis with respect to an intended inspection item.
The sampling pump for the automatic chemical analyzer as described above is a cylinder pump as shown in FIG. 1. The cylinder pump comprises a cylindrical holder 10 and a cylindrical glass cylinder 11 fitted in the holder 10. In the glass cylinder 11 is slidably inserted a plunger 13 with O-rings 12 of an elastic material used as seal members. The holder 10 has a cap 14 fitted at the end, and liquid is withdrawn and discharged through a hole 14a in the cap 14. In this prior art cylinder pump, the O-rings 12 are deformed randomly as they slide in frictional contact with the galss cylinder 11 when the plunger 13 operates. The deformation of the O-rings 12 results in subtle changes in the quantity of the liquid withdrawn or discharged. In addition, the frictional resistance of the O-rings 12 is not the same at all time. Therefore, where the plunger 13 is driven by, for example, a pulse motor, the motor is not stopped at a given rotational position because the frictional resistance per se of the O-ring is not always constant and the accuracy with which the liquid is withdrawn and discharged is impaired. The chemical analyzer, where a multi-ganged cylinder pump is driven by a single motor, cannot accurately analyze samples since the quantities of the liquid withdrawn or discharge inevitably changes.
Further, the O-rings which are made of an elastic material are worn out during repetitive use. The flakes portions of worn-out O-rings get into a flow path of the apparatus, clogging electromagnetic valves, check valves, nozzles, etc. to cause operation errors. This also deteriorates the accuracy of measurement.